This invention relates generally to thermal spray apparatus and particularly to a dual wire, arc type of thermal spray gun.
Thermal spraying is a process of melting and propelling fine particles of molten material such as metal to form a coating. One type of thermal spray gun is a dual wire, arc thermal spray gun in which two wires are fed into electrical contact at the wire ends. The ends are melted by an electrical arc with current passed through the wires. A jet of compressed gas (usually air) is blown through the arc zone to atomize (i.e. nebulize) the molten metal and effect a spray stream of molten metal particles. Arc current can be of the order of hundreds of amperes. Typically the power is brought through cables connected to feed rollers and/or wire guides in the gun that electrically contact the wires and guide them to the point of arcing.
Wire guides are used to both guide the wire to the arc zone and to transfer electrical energy from the DC power source to the wire. Because they need to be efficient conductors of electricity, they are usually made of copper or copper-base alloys. Due to the friction of the feedstock wire, some of which can be extremely abrasive, wire guides need to be changed on a frequent basis.
Various configurations for jetting the atomizing air to the melting wire tips have been used in efforts to provide an effective spray stream, and for introducing auxiliary air to modify and improve the spray stream, for example as taught in U.S. Pat. No. 5,964,405 (Benary et al.) However, there has remained a need for improvement in the wire guides. In the existing art, the wire guides are screwed into a stationary wire guide that requires a tool in order to replace the guide. On production lines where the spray guns are used, it may take an average of five minutes to change the wire guides in one spray gun. This is true if there are no problems, such as binding between the threaded portion of the wire guide. In an effort to properly align the wire guides, a technician may use a tool to bend the wire guide after it has been screwed into place. This can cause difficulty when the time arrives for replacement of the wire guide. Some companies have several spray guns on line, and may need to shut down production for a significant amount of time between each guide change-over. Accordingly, a need exists for an improved spray gun having wire guides that can be changed relatively quickly.
The present invention relates to an improved, dual wire, arc thermal spray gun that allows the user to change the wire guides without the need for any tools. The wire guides may be removed and replaced by hand without screwing them into place. An arc thermal spray apparatus of the present invention generally includes a spray gun body housing, a pair of wire guides that can receive wire, and a gas cap or nozzle attached to the body adjacent the wire guides. The wire guides are positioned so that their ends converge to guide the two metal wires to a point of contact at their spraying tips. A gas tube is positioned in the gun body on an axis located centrally with respect to the stationary wire guides, and is used to channel gas such as air to the spraying tips. A retainer is attached to the gun body coaxially with the central axis to hold the removable wire guides in place. The gas cap is attached to the gun body coaxially with the central axis to serve as a nozzle and to hold the retainer in position with respect to the removable wire guides.
The removable wire guides can be removed from the stationary wire guides without the use of a tool. The user can quickly change the removable wire guides by simply removing the gas cap and retainer, and pulling the removable wire guides from the stationary wire guides housed by the gun body. A fresh pair of removable wire guides are pushed into the stationary wire guides so that they are temporarily frictionally retained by the O-rings seated within the stationary wire guides, and the retainer slides over the guides and gas cap is reattached to the gun body. The relatively quick ability to change wire guides results in significant time savings. Further, the retainer ensures optimal alignment of the removable wire guides.